1. Technical Field
The present invention relates to a composite material turbine engine blade having a brush joint at its free end, as well as to its production process. The invention is used in the aeronautical field.
2. Discussion of the Prior Art
In order to ensure maximum performance characteristics in a aircraft turbine engines, it is indispensable to limit to the greatest possible extent gas leaks between the fixed components and rotary components of said engines. Thus, it is more specifically necessary to limit gas leaks in the fan, low pressure compressor and high pressure compressor of said turbine engine.
FIG. 1 diagrammatically shows an aircraft turbine engine having, in conventional manner, a low pressure compressor 1, a high pressure compressor 3 and a fan 5. The high pressure compressor 3 has a fixed part, namely the stator 3a, whose blades 3b are held by their ends fixed to the casing 2. It also has a rotary part, namely the rotor 3c, whose blades 3d are fixed by their ends fixed to the rotary disks 3c. In the same way, the low pressure compressor 1 has a fixed stator 1a and a rotary rotor 1b. Moreover, the fan 5 has a rotary blade 6 and a fixed part, the casing 7.
In order to improve the performance characteristics of such turbine engines, the aim is to limit gas leaks between the various rotary components and the fixed components by using seals.
For example, for low and high pressure compressors 1, 3, the aim is generally to limit gas leaks between the stator and rotor. In the case of the fan 5, the aim is to limit gas leaks between the blades 6 and the casing 7.
At present, several seal types are known to the expert. One of these seals is made from an abradable material, i.e. a material having dimpled structures of a honeycomb type, which is positioned on the fixed components of the turbine engine (on the casings or stators) to the right of the rotary components (rotor or blade). FIG. 2 shows one of the seals made from an abradable material.
FIG. 2 shows in longitudinal sectional form a seal of this type applied to a fan. Thus, FIG. 2 diagrammatically shows a fan portion 5 having a casing 7 and a rotary blade 6. The casing 7 houses a seal 8 positioned to the right of the blade 6. This seal 8 is made from an abradable material of the honeycomb type.
However, under the action of the centrifugal and axial forces exerted on the blade 6 and due to the expansion of the materials as a function of ambient temperature, friction of the blade 6 on the abradable seal 8 can lead to a deterioration of the latter, as a result of the relatively fragile constitution of the abradable material. In addition, when the rotation speed of the blade 6 is reduced, the forces and temperature inevitably decrease, so that between the fixed components (namely the casing 7 in FIG. 2) and the rotary components (namely the blade 6) there is a leakage flow into the deteriorated area of the seal 8. This deteriorated zone then constitutes a clearance J between the casing 7 and the blade 6.
Another abradable material seal type is described in FR-A-2 660 371. This document relates to a sealing arrangement placed between the stages of the rotor blades. This sealing arrangement is obtained with a honeycomb material.
Abradable material seals are also described in FR-A-2 563 571, U.S. Pat. No. 4,227,703 and FR-A-2 481 740. These documents describe seals fixed to the rotary components of turbine engines. According to these documents, the blades of the compressors or fan are covered on their free ends with an abrasive coating. Such seals have disadvantages similar to those referred to in connection with FIG. 2, namely that said seals can easily be deteriorated as a result of their constitution, when the seals rub on the fixed components of the turbine engines.
The use of brush joints as seals is also known for limiting gas leaks in turbine engines. Thus, e.g. FR-A-379 209 describes different stages of turbines having mobile blades at the free end of each of which is added a ring equipped with a brush joint. However, such a brush joint is simply connected to the free end of the blade. Moreover, during sudden changes of engine speed or in the case of a sudden contact with the fixed part, the brush joint can be torn away from said blade. The brush joint which is then free within the turbine engine can obviously give rise to serious damage.
Numerous other document such as FR-A-2 477 226, EP-A-169 394 and FR-A-2 691 749 describe seals constituted by brush joints connected to the rotors. The disadvantages of these brush joints are substantially identical to those of the brush joint of FR-A-379 209.